Capturing wide-field retinal images is traditionally a very challenging process. Because of the basic anatomy of the human eye, imaging the retina requires illumination of the retina with an external light source projecting illumination through the patient's pupil while simultaneously capturing a retinal image through the same pupil while avoiding or minimizing glare from the light source.
Pupil dilation techniques are able to create a much larger pupil opening for examination purposes. Even so, very precise alignment is needed for retinal imaging even with pupil dilation. The distance that the imaging system is positioned from the front of the cornea is particularly critical, as being either too far away or too close will result in corneal glare from the light source. Therefore, stationary tabletop retinal imaging systems are generally much easier to operate than handheld retinal cameras because of the precise alignment and enhanced stability provided by a tabletop system.
Tabletop retinal imaging systems are, expensive and difficult to move. Therefore tabletop systems are not well-suited to use in the field, in remote clinics, or in multipurpose examination clinics lacking dedicated ophthalmological equipment. Accordingly, various companies and educational institutions have started to develop and conduct clinical trials utilizing simple and inexpensive smartphone attachments that allow for the capture of retinal images. These attachments range from simple brackets that hold an ophthalmic lens in front of a smartphone to small devices that place a light source suitable for illuminating the retina very close to the smartphones camera lens to allow retinal images to be captured using the camera's existing optics.
Unlike traditional retinal imaging systems, the retinal images that are captured with smartphone attachments of this nature can appear anywhere on the smartphone image sensor, and the position of the useable portion of the retinal image can continuously move around on the image sensor during the retinal exam since a smartphone-based imaging system is typically handheld. In addition, the field of view of retinal imaging systems greatly influences the ease of use of these systems. In particular, camera systems that have a narrower field of view inherently require less precision in terms of alignment position and working distance than wider field of view camera systems. Because of this, handheld camera systems, including smartphone-based systems, generally have a considerably narrower field of view than stationary tabletop systems that provide a chin rest to keep the patient's head from moving during the exam. Unfortunately, retinal screening for medical conditions requires a much wider field of view than typical hand-held camera or smartphone-based system can readily provide.
The use of panorama image preparation can in certain instances remedy and inherently narrow field of view. Traditional retinal image panorama construction requires the camera operator to capture multiple still shots of various regions of the eye, and to run a post-image acquisition process in which the operator manually selects images that are believed can be suitably stitched together by software designed to construct the image panorama. Thus panorama preparation is typically performed after the patient exam. This process has several problems, the main one of which is that the camera operator may find out that the images that they have captured are not adequate for construction of the panorama until after the patient's exam has been completed and they are already working with the next patient.
The embodiments disclosed herein are directed toward overcoming one or more of the problems noted above.